Ford 5000 selectomatic

Anyone please help.. I have a 1967 Forrd 5000 with a selectomatice transmission..I have lost R1,3,4,7,and 8th gears...What will cause this??? It's been a while since i ran the tractor due to tearing it down for overhaul. As far as i can remember i have R1, 1,2,5,9 and 10th gears...PLEASE HELP!!!!!